Alright, let's solve this math problem step by step. First, we have the number 13. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 40. So, we're going to take the number 13 and add it to itself 40 times.
Step 1: 0 + 13 = 13
Step 2: 13 + 13 = 26
Step 3: 26 + 13 = 39
Step 4: 39 + 13 = 52
Step 5: 52 + 13 = 65
Step 6: 65 + 13 = 78
Step 7: 78 + 13 = 91
Step 8: 91 + 13 = 104
Step 9: 104 + 13 = 117
Step 10: 117 + 13 = 130
Step 11: 130 + 13 = 143
Step 12: 143 + 13 = 156
Step 13: 156 + 13 = 169
Step 14: 169 + 13 = 182
Step 15: 182 + 13 = 195
Step 16: 195 + 13 = 208
Step 17: 208 + 13 = 221
Step 18: 221 + 13 = 234
Step 19: 234 + 13 = 247
Step 20: 247 + 13 = 260
Step 21: 260 + 13 = 273
Step 22: 273 + 13 = 286
Step 23: 286 + 13 = 299
Step 24: 299 + 13 = 312
Step 25: 312 + 13 = 325
Step 26: 325 + 13 = 338
Step 27: 338 + 13 = 351
Step 28: 351 + 13 = 364
Step 29: 364 + 13 = 377
Step 30: 377 + 13 = 390
Step 31: 390 + 13 = 403
Step 32: 403 + 13 = 416
Step 33: 416 + 13 = 429
Step 34: 429 + 13 = 442
Step 35: 442 + 13 = 455
Step 36: 455 + 13 = 468
Step 37: 468 + 13 = 481
Step 38: 481 + 13 = 494
Step 39: 494 + 13 = 507
Step 40: 507 + 13 = 520

So, 13*40 = 520